Researchers have made an important breakthrough in the search for earlier ways to detect Alzheimer’s disease.
For the first time, a large study has shown that blood markers linked to Alzheimer’s can be found in healthy middle-aged adults and are associated with subtle changes in thinking and memory years before dementia develops.
The study was led by researchers at the University of California, San Francisco (UCSF) and was published in The Lancet. The findings suggest that a simple blood test could one day help identify people at increased risk of Alzheimer’s long before symptoms become obvious.
Alzheimer’s disease is the most common cause of dementia worldwide. The condition gradually damages brain cells, leading to memory loss, difficulties with thinking, and problems carrying out everyday activities.
By the time symptoms appear, significant brain damage has often already occurred. For this reason, scientists have been searching for ways to detect the disease much earlier.
Two proteins play a central role in Alzheimer’s disease: amyloid and tau. In people with Alzheimer’s, amyloid proteins accumulate and form sticky plaques between brain cells, while tau proteins build up inside cells and create tangles. These changes can begin many years, and sometimes decades, before memory problems become noticeable.
Traditionally, detecting these proteins has required expensive brain scans or spinal fluid tests. While these methods can be effective, they are not practical for large-scale screening because they are costly, invasive, or difficult to access. Blood tests offer a much simpler alternative and have attracted growing attention from researchers around the world.
The UCSF team studied 1,350 adults between the ages of 53 and 69 who did not have dementia. Participants were part of the long-running CARDIA study, which follows adults over many years to understand factors that influence health and aging. About 58 percent of participants were women, and nearly half were Black.
Researchers measured blood levels of amyloid and tau proteins and compared them with participants’ performance on cognitive tests. They found that approximately 6 percent of participants had elevated levels of both proteins, suggesting early Alzheimer’s-related changes in the brain.
Even though these individuals did not have dementia, they performed slightly worse on tests measuring processing speed and executive function. Processing speed refers to how quickly a person can understand and respond to information.
It plays an important role in everyday tasks such as driving, following conversations, and reacting to changing situations. Executive function includes skills such as planning, organizing, problem-solving, and managing complex activities.
The researchers then followed participants for five years to see how their thinking abilities changed over time. The results were striking.
Individuals with elevated amyloid and tau levels were between 2.5 and 4 times more likely to experience rapid decline in verbal memory. They were also about 3 to 4 times more likely to experience rapid declines in processing speed.
These findings suggest that subtle changes in thinking may appear much earlier than previously recognized. Rather than memory loss being the first sign, slower thinking speed and difficulties with planning and organization may emerge before more obvious symptoms develop.
The study is especially important because it supports the growing idea that Alzheimer’s disease begins long before a clinical diagnosis is made. Researchers believe that identifying people during these early stages could create opportunities to reduce risk and potentially delay disease progression.
Senior author Dr. Kristine Yaffe noted that addressing modifiable risk factors may play a major role in prevention. Previous research has shown that factors such as physical inactivity, smoking, depression, poor cardiovascular health, and limited cognitive engagement may contribute to dementia risk.
Some experts estimate that up to 40 percent of dementia cases could potentially be delayed or prevented by addressing these factors.
The findings also highlight the promise of blood-based testing. Compared with brain scans and spinal taps, blood tests are relatively inexpensive, widely available, and less invasive.
However, researchers caution that these tests are not perfect. False positive results can occur, and the biomarkers only detect Alzheimer’s-related changes rather than other causes of dementia.
One of the strengths of this study is its large and diverse participant group, along with long-term follow-up. However, additional research will be needed to determine how accurately these blood tests can predict future dementia and whether early interventions based on test results can improve outcomes.
Overall, the findings provide encouraging evidence that Alzheimer’s disease may be detectable years before symptoms emerge. While routine screening of healthy adults is not yet recommended, the research moves scientists closer to a future where earlier detection and prevention strategies may help reduce the burden of this devastating disease.
Source: University of California, San Francisco (UCSF).
